The present invention relates to a method of driving a plasma display panel (PDP) of three-electrode AC type or, in particular, to a technique for resetting each cell of the PDP to a predetermined state.
The AC-type PDP continues to discharge and emit light for display in accordance with a voltage waveform applied alternately to two sustaining electrodes thereof. Each session of discharge is completed within 1 .mu.s to several .mu.s from the pulse application. The ions that are the positive charge generated by the discharge are accumulated on the surface of an insulating layer on an electrode supplied with a negative voltage. In a similar fashion, the electrons which are negative charge are accumulated on the surface of an insulating layer on an electrode supplied with a positive voltage.
If a wall charge is initially generated by a discharge with a pulse (write pulse) of a high voltage, followed by application of a pulse (a sustaining pulse or a sustaining discharge pulse) of a voltage (sustaining voltage or a sustaining discharge voltage) lower than and having a different polarity from the preceding voltage, then the pulse is superposed on the wall charge previously accumulated, and increases the voltage of the discharge space to such an extent that the discharge starts over a threshold value of the discharge voltage. Specifically, a cell, once gaining a wall charge by a write discharge, sustains the discharge when supplied with alternate sustaining pulses of opposite polarities. This is called the memory effect or the memory function. Generally, the AC-type PDP uses this memory effect for display.
The AC-type PDP is of two types, one a two-electrode type in which selective discharge (addressing discharge) and sustaining discharge are carried out with two electrodes, and the other a three-electrode type in which a third electrode is used for addressing discharge. In the color PDP for effecting gradation display, the phosphor material formed in the discharge cell is excited by the ultraviolet light generated by the discharge. The disadvantage of this phosphor material is that it easily succumbs to the impact of ions making up the positive charge generated at the same time as the discharge. The PDP of a two-electrode type is so configured that the phosphor material comes into direct contact with ions, which is liable to shorten the life of the phosphor material. In order to avoid this inconvenience, the color PDP generally uses the three-electrode structure utilizing the surface discharge. The PDP of three-electrode type is further classified into a configuration in which the third electrode is formed on the same substrate that the first and second electrodes for sustaining discharge are arranged on and a configuration in which the third electrode is arranged on the other substrate in opposed relation to the first substrate. The configuration in which three electrodes are formed on the same substrate is also subdivided into a configuration in which a third electrode is arranged on the two electrodes for sustaining discharge and a configuration in which a third electrode is arranged under the other two electrodes. Further, the visible light emitted from the phosphor material is either transmitted through the phosphor material (transmission type) or reflected from the phosphor material (reflection type). The present invention is applied to the three-electrode AC-type PDP. An explanation will be given with reference to the reflection type of PDP comprising a panel including a third electrode formed on a substrate in opposed relation to the substrate of the sustaining discharge electrodes, in which a part of the sustaining electrode is formed of a transparent electrode.
In the conventional method of driving a three-electrode AC-type PDP based on the "write addressing method of addressing/sustaining discharge period separation type", each subfield is configured of a reset period, an addressing period and a sustaining discharge period, and a self-erasure discharge is caused by applying a reset pulse of high voltage so that all the cells discharge during the reset period. The light emission by the application of the reset pulse and the light emission by self-erasure discharge also contribute to the display. The light emission at all the cells regardless of the specific contents of the display increases the background brightness for a reduced contrast. Also, for gradation display in the PDP apparatus, each frame is segmented into a plurality of subfields, and the frequency of the sustaining discharge in each subfield is changed in accordance with the weight of the brightness. With a subfield of small weight, for example, the sustaining discharge is effected only several times. The light emission at all the cells, therefore, deteriorates the linearity of gradation display. In recent years, the display quality of the PDP apparatus has been improved to such an extent that the deterioration of display quality due to the fact described above has begun to pose a problem.